A method such as injection molding or compression molding has hereto been used for preparing a vessel from a thermoplastic resin. This method, however, is not suited for preparation of a vessel which is, for example, made of a highly foamed resin. This is because, in this method, the resin is so strongly compressed in the mold that the resin is prevented from high foaming. Therefore the injection molding method can not make a highly foamed article. As a result, in order to obtain a vessel of a highly foamed thermoplastic resin, a method must be adopted in which a highly foamed resin sheet is at first prepared and then the sheet is fabricated into a vessel. However, there has not been hitherto an efficient method for preparing a vessel by using a highly foamed resin sheet as the material. The present invention has been made in view of the above fact.